This application is based on Application No. 2001-121195, filed in Japan on Apr. 19, 2001, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a Sn based alloy containing a Snxe2x80x94Ti compound that is used for manufacturing a Nb3Sn superconducting wire by an internal diffusion method, and a method for manufacturing the same. The present invention also relates to a precursor of the Nb3Sn superconducting wire using the Sn based alloy.
2. Description of the Related Art
A method using a Nb3Sn compound prepared by an internal diffusion method has been proposed for manufacturing superconducting wire. In the internal diffusion method, a precursor of the Nb3Sn superconducting wire called a module is prepared by integrating a metallic Sn rod at the center of a Cu base metal in which a number of metallic Nb rods are integrated so that they do not make direct contact with each other. The module is heated at about 650xc2x0 C. and drawn so that Sn reacts with metallic Nb by heat diffusion of the Sn to finally obtain the Nb3Sn wire useful as a superconducting wire material. For improving the superconductive characteristics of the Nb3Sn superconducting wire, prepared by the internal diffusion method, in a high magnetic field, a Sn based alloy containing a Snxe2x80x94Ti compound is prepared by adding Ti into the Sn base metal. It is known in the art that this Sn based alloy has better superconducting properties than Nb3Sn wire using metallic Sn. However, the Sn based alloy containing the Snxe2x80x94Ti compound as used herein involves the problem of generating defects due to the mingling of non-molten Ti and Ti oxide into the Sn based alloy during the conventional melt-casting process, because the difference between the melting points of Sn (232xc2x0 C.) and Ti (1670xc2x0 C.) is substantially large for manufacturing the Sn base containing Ti, and Ti is liable to be oxidized during the process.
A proposed method for manufacturing a defect-free Sn based alloy containing the Snxe2x80x94Ti compound comprises, for example, melting Sn by heating at 600 to 1750xc2x0 C. under an inert gas atmosphere, adding 0.3 to 6.5% by weight of Ti relative to the content of Sn, and casting the mixture into a mold made of cast iron or stainless steel at 500 to 1750xc2x0 C. (Japanese Patent Publication No. 6-76625).
However, since the Snxe2x80x94Ti compound is not finely dispersed in the Sn based alloy which was melted under an inert gas atmosphere and cast by using the cast iron or stainless steel mold, improved superconductive characteristics cannot be expected. In addition, since the Sn based alloy containing the Snxe2x80x94Ti compound produces so large shrinkage cavity, manufacturing yield of the Sn based alloy containing the Snxe2x80x94Ti compound becomes poor. Therefore, some improvements have been desired in the method for manufacturing the Sn based alloy containing the Snxe2x80x94Ti compound.
Accordingly, it is an object of the present invention to provide a method to solve the above problems in the conventional manufacturing methods. A further object of the present invention is to provide a Sn based alloy containing a Snxe2x80x94Ti compound in which granules of the Snxe2x80x94Ti compound having a fine particle diameter are uniformly dispersed where permitting the cast ingot to be free from forming the shrinkage cavity, as well as a method for manufacturing the Sn based alloy containing the Snxe2x80x94Ti compound uniformly dispersed therein.
The present invention provides a Sn based alloy containing a Snxe2x80x94Ti compound prepared by adding 0.1 to 5% by weight of Ti relative to the content of Sn, wherein the particles of the Snxe2x80x94Ti compound have a maximum diameter of 30 xcexcm or less and a mean diameter of within a range of 5 to 20 xcexcm.
The present invention also provides a method for manufacturing a Sn based alloy containing a Snxe2x80x94Ti compound finely dispersed therein, comprising the steps of melting Sn by heating at 1300 to 1500xc2x0 C. in vacuum or under an inert gas atmosphere, adding 0.1 to 5% by weight of Ti relative to the content of Sn followed by melting the mixture by heating at 1300 to 1500xc2x0 C., and casting the molten liquid into a mold made of copper.
The present invention further provides a method for manufacturing a Sn based alloy containing a Snxe2x80x94Ti compound finely dispersed therein, comprising the steps of melting Sn by heating at 1300 to 1500xc2x0 C. in vacuum or under an inert gas atmosphere, adding 0.1 to 5% by weight of Ti relative to the content of Sn followed by melting the mixture by heating at 1300 to 1500xc2x0 C., and casting the molten liquid into a mold made of copper through a carbon pouring cup mounted on the copper mold.
The present invention further provides a precursor of a Nb3Sn superconducting wire having a structure in which a number of the Nb metal materials and Sn based alloys containing the finely dispersed Snxe2x80x94Ti compound are integrated in a copper based metal so that they do not make direct contact with each other.